Intraoperative neuromonitoring for removal of large vestibular schwannoma: Facial nerve outcome and predictive factors.

BACKGROUND: Preservation of facial nerve (FN) function is one of the major goals for resection of large vestibular schwannoma (VS) (≥ 30 mm). Little is known about the FN outcome and its predictive factors due to limited data.

OBJECTIVE: To explore the predictive factors affecting FN outcome following resection of large VS.

METHODS: 106 Large VS patients underwent surgical resection from 2010 to 2012 via intraoperative neuromonitoring for FN preservation approach. Postoperative FN function evaluation was conducted at the time points of 3-7th day, 3rd month and at the end of the 2nd year. Correlation between tumor size, intraoperative parameters and FN function were examined.

RESULTS: The ratios of total and subtotal resection were 82.1% and 14.2%, respectively. Acceptable FN function was achieved in 78% patients. Patients with good FN function showed much smaller (P < 0.01) VS size than those of poor-FN function patients at 3-7th day, 3rd month and 2nd year. There was a significant correlation between facial motor evoked potential (FMEP) ratios and postoperative FN function at 3-7th day (r = -0.709, P < 0.001) 3rd month (r = -0.709, P< 0.001) and 2nd year (r = -0.750, P < 0.001). Maximal response amplitude (MRA) ratio was a supplementary indicator for train time in predicting both immediate and long-term FN function in patients with large VS.

CONCLUSION: Indicative factors of both immediate and long-term postoperative FN function in large VSs include tumor size, intraoperative train time, start to final FMEP ratios and proximal to distal MRA ratios.